Recently, superconductive compositions including mixed oxides of rare earth, alkaline earth and copper metals have been discovered. For example, Wu et al., Physical Review Letters, Vol. 58, No. 9, pages 908-910 (1987) and Hor et al., Physical Review Letters, Vol. 58, No. 9, pages 911-912 (1987), disclose Y-Ba-Cu-O compound systems exhibiting superconductivity. Additionally, in Physical Review Letters, Vol. 58, No. 18 (1987), Moodenbaugh et al. (pages 1885-1887), Murphy et al. (pages 1889-1890) and Hor et al. (pages 1891-1894) disclose additional rare earth, alkaline earth, copper metal mixed oxide compositions exhibiting superconductive properties. Additional rare earth, alkaline earth, copper mixed metal oxides are disclosed by Er-Rakho et al., Journal of Solid State Chemistry, Vol. 37, pages 151-156 (1981). Generally, these references disclose the formation of the rare earth, alkaline earth, copper mixed metal oxide compositions by sintering the individual oxide powders. Hakuraku et al, Appl. Phys. Lett., Vol. 52, No. 18, May 1988, pages 528-530, disclose superconducting Y-Ba-Cu-O compounds further including fluorine. Hakaraku et al disclose that the fluorine strengthens the superconductive connections among the grains of the material.
Additionally, rare earth-free thallium or bismuth containing materials have also been discovered which exhibit superconductive properties. Examples of these materials comprise Tl-Ba-Cu-O compounds such as Tl.sub.2 Ba.sub.2 CuO.sub.6 and Tl-Ca-Ba-Cu-O compounds such as Tl.sub.2 CaBa.sub.2 Cu.sub.2 O.sub.8 and Tl.sub.2 Ca.sub.2 Ba.sub.2 Cu.sub.3 O.sub.10. Recent efforts in this area are summarized by Dagani, Chemical and Engineering News, May 16, 1988, pages 24-29.
Continual investigations are being made to discover additional superconductive compositions, superconductive compositions which exhibit superconductivity at higher temperatures and superconductive compositions which are stabilized against attack and degradation by moisture and by carbon dioxide.